1. Field of the Invention
This invention relates to catheters, and in particular to dilitation balloon catheters, for use in the performance of percutaneous transluminal procedures including peripheral angioplasty, coronary angioplasty and valvuloplasty. The configuration of the catheter permits the introduction of a relatively large caliber balloon across a severe intraluminal stenosis with relative facility.
2. Description of the Prior Art
In 1977 Dr. Andreas Greuntzig first used a balloon-tipped flexible catheter to percutaneously dilitate a region of stenosis within a coronary artery of a patient with atherosclerotic heart disease. Since that time, the incidence of percutaneous transluminal coronary angioplasty has increased exponentially. Over the course of the past three to four years, the performance of this procedure has become routine within many major medical centers throughout the world. With the advent of improved technology and operator skill, the indications for this procedure have also increased substantially.
At the outset of a routine percutaneous transluminal coronary angioplasty procedure, a preshaped angioplasty guiding catheter containing a balloon catheter equipped with a flexible intracoronary guidewire is engaged within the ostium of a coronary vessel containing the lesion to be dilitated. Once suitably engaged (within the left main or right coronary ostium), the guidewire is advanced within the lumen of the appropriate vessel and manipulated across the region of stenosis. By rotating the guidewire, which contains a slight bend within its distal aspect, the operator can control the course of the wire, selecting the appropriate coronary lumen as the wire is advanced.
Once the wire is positioned across the region of stenosis (narrowing), the angioplasty dilitation balloon catheter is advanced over the guidewire and positioned across the stenotic lesion. The angioplasty is accomplished by inflating the dilitation catheter to a high pressure, typically 6 to 10 atmospheres. Generally, 3 to 4 dilitations are required for each region of stenosis. Balloon inflation is maintained for 30 to 90 seconds during each dilitation, depending upon anatomic considerations and operator preference.
Following the final dilitation, the guidewire and balloon catheter are withdrawn leaving the guiding catheter in place. (Frequently, an exchange wire is installed within the lumen of the coronary artery via the guiding catheter prior to removal of the balloon catheter. This ensures intraluminal access in the event of a complication.) Selective coronary angiography then is performed to evaluate the cosmetic appearance of the vessel following the angioplasty and to determine the severity of the residual stenosis.
At present, the major obstacle to the performance of an angioplasty procedure involves the manipulation of the angioplasty dilitation balloon catheter across the region of stenosis within the coronary artery. Although the guidewire can frequently be advanced across the region of stenosis with relative facility in vessels which are anatomically amenable to the performance of an angioplasty (see FIG. 1A), manipulation of the balloon catheter across the stenosis often proves difficult because the cross-sectional profile of the deflated balloon affixed to the distal aspect of the dilitation catheter is considerably greater than the corresponding profile of the intracoronary guidewire. Advancing the relatively large caliber angioplasty catheter within a significant stenosis commonly results in disengagement of the guiding catheter from the coronary ostium. Once the guiding catheter becomes disengaged, the angioplasty catheter frequently prolapses within the sinus of Valsalva immediately cephaled to the aortic valve, precluding further advancement of the angioplasty catheter (see FIG. 1B). The guiding catheter disengages in this circumstance because it is moderately flexible. It must be flexible because insertion of this catheter requires that it be advanced over a guidewire up the aorta, which is relatively straight, and then over the aortic arch, which is, as the name implies, curvilinear.
One approach to circumvent this problem involves the development of angioplasty dilitation balloon catheters that impart less resistance during manipulation across a coronary stenosis relative to conventional profile dilitation catheters. The approach to the development of these angioplasty catheters has, in essence, involved the miniaturization of conventional balloon catheters. These "low profile" catheters have substantially contributed to the feasibility of performing angioplasty individuals with severe coronary stenoses previously considered unsuitable for percutaneous transluminal coronary angioplasty.
FIG. 2 illustrates the basic configuration of a conventional angioplasty balloon catheter. The catheter consists of a lumen to accommodate a guidewire, an inflation channel, as well as a small dilitation balloon affixed to the distal aspect. Attempts to miniaturize these conventional catheter systems has resulted in several disadvantages, given the constraints imposed by current technology and material availability. For example, the balloons of these "low profile" systems tend to have a correspondingly smaller inflated diameter relative to conventional balloons. This circumstance derives from the fact that the most suitable material for the construction of dilitation balloons must be relatively inelastic. Thus, the use of these "low profile" catheters frequently obligates the operator to install one or more dilitation balloon catheters of sequentially larger caliber. In addition to the added expense, radiation exposure and operative time that this approach involves, the complication rate for an intravascular procedure is in direct proportion to the number of catheters employed during the procedure, as well as the time required to complete the operation.
Despite extensive research and development, the deflated profile of these "low profile" catheters remains substantial, hence the resistance imparted by these devices during manipulation within a coronary stenosis remains considerable. Furthermore, the introduction of a "low profile" catheter of conventional configuration within a region of stenosis commonly deforms the deflated balloon resulting in the development of wrinkles which further contribute to the resistance generated by the catheter (see FIGS. 2C and 2D).
To circumvent the problems intrinsic to miniaturizing the balloon component of the catheter, the Hartzler system was developed wherein the caliber of the guidewire was reduced relative to the other components of the system. Because this results in a fragile guidewire, the system was designed such that the guidewire could not be removed from the protective confines of the dilitation balloon catheter lumen. Disadvantages of this system include the inability to accommodate conventional guidewires that afford relatively superior directional control and the maintenance of a guidewire within the coronary artery during the process of exchanging dilitation balloon catheters.
The configuration of the Hartzler system does permit rotation of the guidewire about the axis of the catheter and this feature affords some, albeit suboptimal, directional control to the catheter system. The configuration of the Hartzler system, however, does not permit (1) 360.degree. rotation of the guidewire, and (2) independent movement of the guidewire relative to the catheter along the axis of the system. Because the caliber of the Hartzler balloon is relatively small, when fully inflated, use of this device frequently mitigates the use of one or more subsequent dilitation balloon catheters of sequentially larger caliber in order to achieve an optimal result. Because the Hartzler system does not accommodate an exchange wire, the operator must completely renegotiate the course of the diseased coronary artery with another intracoronary guidewire before advancing the subsequent larger caliber angioplasty dilitation balloon catheter across the region of stenosis. This inability to use an exchange wire enhances the difficulty of the procedure and thus predisposes the patient to increased risk. Many operators prefer to install an exchange wire within a coronary artery during the process of exchanging dilitation balloon catheters to ensure intraluminal access in the event that a complication occurs during the process. The use of the Hartzler system does not permit this.
Although conventional "low profile" catheter systems can accommodate an exchange wire, there exist some intrinsic disadvantages to these catheter systems relative to the Hartzler system. The deflated profile of conventional low profile systems tends to exceed the corresponding profile of the Hartzler system. Hence, it is frequently more difficult to advance one of the these catheters across a region of critical stenosis relative to the Hartzler system. Secondly, the lumen of low profile catheters cannot accommodate the larger caliber intracoronary guidewires. Given the fact that torque control and hence, directional control are directly related to the caliber of the guidewire, the use of conventional low profile catheter systems requires the use of guidewires with suboptimal directional control. This feature further limits the likelihood of success in the performance of an angioplasty of a complete coronary occlusion (wherein the use of a low profile catheter system would be optimal). Most operators prefer to use relatively large caliber (0.018 inch) intracoronary guidewires in the performance of an angioplasty of a complete coronary occlusion because of the enhanced column strength that this increased caliber affords, and small caliber guidewires tend to buckle in this circumstance. While one would prefer to use a low profile system in this situation, the fact that these systems do not accommodate a stiff wire tends to mitigate against their use in this circumstance.